1. Field of the Invention
The present invention relates in general to holography and, in particular, to a phase volume hologram and method for producing the phase volume hologram.
2. Description of Related Art
Phase volume holograms made from a polymer body that exhibits local variations of refractive index in conformity with the intensity of a recorded interference pattern are well known in the literature. These holograms are generally recorded in different layers of photopolymers and have an achievable level of refractive index modulation (Δn) near 3×10−2. However, these holograms are usually made from organic materials that have low mechanical properties and low thermostability and, as such, are not very reliable or durable. For more information about these types of holograms reference is made to an article by William J. Gambogi et al. entitled “Advances and Applications of DuPont Holographic Photopolymers” Optics Quebec '93, Conf. 2043, August 1993. This article is hereby incorporated by reference herein.
Also well known in the literature are phase volume holograms made from a porous siliceous body completely filled with a solid-phase polymeric material that exhibits local variations of refractive index in conformity with the intensity of a recorded interference pattern. These holograms have better mechanical properties and optical properties than the aforementioned holograms recorded in a polymer body. However, these holograms have an achievable level of refractive index modulation (Δn) that is not very high, ˜3.5×10−3. For more information about these types of holograms reference is made to the following documents which are incorporated by reference herein:                Melinda G. Schnoes et al. “Photopolymer-Filled Nanoporous Glass as a Dimensionally Stable Holographic Recording Medium” Optics Letters, Vol. 24, No. 10, pp. 658-660, May 15, 1999.        N. S. Shelechov “Optical Composites Based on Porous Silica glasses” Optica Applicata, Vol. XXIV, No.1-2, pp. 27-35, 1994.        PCT Patent No. WO 99/15939 entitled “Volume Phase Hologram and Method for Producing the Same”.        
Accordingly, there is and has been a need for a phase volume hologram that addresses the aforementioned shortcomings and other shortcomings of the traditional phase volume holograms. These needs and other needs are satisfied by the phase volume hologram and method of the present invention.